Many products are transported and sold to an end user in refrigerated condition since they are sensitive to temperature. Moreover, the time from production also has an effect on the quality of the product. For example, dairy products or meat and poultry, as well as medical products, are spoiled as time passes, even if they are at refrigerated temperatures, while they are spoiled extremely quickly when they are in non-refrigerated condition. It is mostly usual to print expiration dates on dairy and meat products. Expiration dates assume a certain temperature and time history and have no indication on the actual time and temperature the product has been exposed to before reaching the end user. This assumption results in either the sale of a spoiled product or premature disposal of good products.
Time-temperature indicators (which will be referred in this text as TTI) are known in the art. These devices are attached to temperature sensitive products at the time of production to monitor the cumulative time/temperature exposure. TTIs are used for monitoring time and temperature exposure of a wide variety of items including food and medical products. Unlike printing expiration dates on products, which are recommendation dates depending on the actual transport and storage conditions that are unknown to the consumer, TTIs respond directly to the temperature to which the product is exposed and reflect the actual temperature history of the product.
Commercial distributors of food and pharmaceuticals commonly attach TTIs to shipping boxes. The most desired use is to ensure the integrity of the cold chain up to the customers that buy and use the product.
The Device may be matched to a particular perishable product or to another particular use. Examples of perishable products for which the use of such device may be useful include, packaged fresh and frozen foods, dairy products, meat, pharmaceuticals, photographic film, canned goods, spices, vitamins, seeds, and plants. Other products that slowly degrade over time, and for which TTIs may be useful, include, for example, paints, coatings, adhesives, caulks etc. TTI's could also be useful as sterilization indicators or as cooking indicators to indicate when a product is sterilized or finished cooking.
Temperature Indicators are basically grouped into two families; a first group that signal a change only after a certain critical temperature has been reached or exceeded (threshold) and a second group that integrate over the entire temperature range and signal a condition at any stage (TTI)
Many attempts have been made and various patents have been issued dealing with devices designed to be attached to a package and to show when a package has been temperature abused or has reached the end of its useful shelf life. Color-change due to chemical reaction is described in many variations and some examples are as follows: an active indicator element that is based on acetylenic compound that changes color is disclosed in U.S. Pat. Nos. 4,737,463; 4,788,151; and 4,789,637. A pH dependent indicator is usually activated due to exposure to actinic radiation that gives rise to chemical change of neutral specie to acidic one and changes color in a time dependent manner. An example is described in U.S. Pat. No. 5,085,802. U.S. Pat. No. 4,812,053 teaches an oxygen sensitive decolorant that reacts with oxygen and is consumed in a TTI manner, that causes the reappearance of the color beneath it. U.S. Pat. No. 3,966,414 describes color change due to radical generation in TTI manner with peroxides. In European patent no. 1026221 and no. 735368, the active cores are redox reactions. Also, there are patents that teach the use of physical change mechanisms. Examples are PCT application no. WO99/44021 or U.S. Pat. No. 5,954,010. Those patents teach the use of material that shrink with changes in temperature, and differs the length of an indicating spring.
One disadvantage of most existing TTIs and the ones described herein is that they must be stored at low temperatures or protected from actinic radiation prior to their attachment to the product. These requirements greatly increase the cost of TTIs, complicate the production line procedures and introduce an element of uncertainty as to the reliability of the indicators. Therefore, there is a need for TTI labels that can be activated at the site of application, or even by the customer himself.
It was desirable to introduce a triggering mechanism. Variations in heat meltable material usually act as an activation trigger and its combination with color change is disclosed in PCT patent applications nos. WO 01/073388 and WO 03/014681. U.S. Pat. No. 4,212,153 and U.S. Pat. No. 5,053,339 describe a laminated indicator with at least two layers that give rise to a perceptible color due to the molecular migration of an agent from an inner layer to an external layer. The reactants are acid base dyes, redox dyes and pH dyes. PCT patent application no. WO 03/014681 describes two reactants; the first one dissolves in a liquid that expands when frozen and is encapsulated. When the product freezes, the capsule fractures (activation trigger) and when the temperature rises, the first reactant reacts with the second reactant that is provided within the housing so that a color develops.
PCT patent application no. WO 87/03367 provides information about application of leuco bases as time-temperature indicator after preliminary exposure to uv radiation.
Although the triggering mechanism is the desirable mechanism that can accurately indicate the temperature history of the product, the above mentioned indicators fail to correctly indicate the past of the product. This is due to the use of the specific chemicals and reactions that are used. Those chemicals are susceptible to environmental influences and therefore are not effective in indicating accurately the condition of the product.
In accordance with the present invention, there is a TTI that is activated by a simple trigger and can be kept at room temperature until activation is needed. The TTI is not sensitive to environmental conditions, such as pH, light, radiation or humidity. The price of such a device is relatively lower and its use is much more efficient than devices that exist nowadays or are described in the patent literature.
TTIs that are used in the present invention are preferably attached to a perishable product and respond to cumulative exposure to time and temperature. Thus, they can provide visual indicia about the true flow of time and history of temperatures that the product has been exposed to, from its manufacturing point until it is sold to and used by the consumer.